In an ink jet imaging process, controlled amounts of one or more fluid ink are delivered to a receptor sheet in a preselected pattern so as to form an image thereupon. In a color imaging process three or more colored inks, and optionally a black pigmented ink are delivered to a receptor sheet by a plurality of separately controlled nozzles. In a number of instances, ink jet imaging is carried out on a receptor sheet which simply comprises a sheet of paper; however, in other instances, it is necessary to carry out ink jet imaging on receptor sheets which comprise coated substrates, and such substrates may comprise paper or polymeric materials. In particular drafting applications, it is necessary that an ink jet image receptor sheet be capable of also being drawn on by a drafting pencil, a pen or a mechanical plotter. It is also desirable that the substrate in such instances comprise a dimensionally stable body of material such as a sheet of polymeric material. The object in providing an ink jet imaging medium suitable for drafting is to provide a medium which, in addition to fulfilling physical requirements such as dimensional stability and transparency, is also capable of receiving both an ink jet image as well as providing a surface which can be drawn upon. Toward that end, a number of formulations have been developed in the prior art.
Ink jet imaging technology has undergone a number of changes, and as a result, an image receptor medium suitable for one generation of imaging process may not be suitable for another. For example, the first generation of ink jet imaging systems employed colored inks which were water based solutions of dyes. These inks were typically applied to the receptor medium from a relatively small number of nozzles. A second generation of ink jet technology employed glycol based solutions of dyes which were also applied to the medium from a relatively small number of nozzles. A third generation of ink jet systems employs water based dispersions of colored pigments which are typically applied from a large number of nozzles. In addition, all of the foregoing systems may or may not employ one or more nozzles for the purpose of dispensing a black pigmented ink. The problem presented is to provide a drafting medium which can work with all three ink jet imaging systems.
A first approach implemented by the prior art was to provide a medium which comprised a substrate having an ink jet ink receptor layer thereupon. The receptor layer comprised a hydrophilic polymer having relatively low water solubility. Typically, such polymers comprise an acrylic resin having a relatively large number of water soluble side chains graft polymerized thereonto. A number of the side chains are cross linked so as to decrease the water solubility of the resultant polymer. This medium has been found to give good image quality for ink jet systems of the first and second generation, namely those employing water or glycol based dye solutions; however, this medium provides very poor color density when utilized in conjunction with the pigment based inks of the third generation. In such instance, image spread of the applied third generation ink is very low; consequently, resultant color density of the image is low.
In a second approach taken by the prior art, a polyelectrolyte material such as polyvinyl pyrrolidone is added to the acrylic based graft polymer previously described. The addition of the polyelectrolyte gives a medium which provides good imaging results with the first and third generation systems, but has low image spread and color density for the glycol/dye inks of the second generation systems.
All of the above-described ink systems are currently employed; thus, it will be appreciated that there is a need for an ink jet imaging medium which provides good results when employed in connection with any of the foregoing ink jet systems. In addition, the medium must be capable of providing a surface which can be marked by other drafting materials such as pencils, pens and plotters. Furthermore, the medium should be relatively easy to prepare and have long term stability. As will be described in detail hereinbelow, the present invention provides an ink jet imaging medium which can be utilized with pigment based and dye based inks having both water and glycol solvents. The medium of the present invention is simple to prepare, stable and low in cost, and provides superior drafting medium. These and other advantages of the present invention will be utterly apparent to those of skill in the art from the discussion, description and examples presented herein.